Atomic nuclei usually possess excitation energies in the keV to MeV range. A notable exception is the 229-Th nucleus where the energy splitting of the ground state doublet is less than 10 eV . This fortuitous coincidence offers prospects for a next-generation clock and for a test of temporal variation of fundamental constants at an unprecedented level of precision. Laser cooling and crystallization of triply charged 229-Th in a linear Paul trap will be reported. The monovalent character of the Th3+ ion is favorable for the isomer level search based on the electron bridge process . The nuclear excitation from the ground-electronic level of a single trapped, cold 229Th3+ ion is expected to be an ideal system for metrological applications.

Highly excited Rydberg atoms have many exaggerated properties. In particular, the atom-atom interaction strength is increased many orders of magnitude over that of atoms in their ground levels. In a mesoscopic ensemble, such strong pairwise interactions can be used for fast preparation of desired many-particle states. Rydberg excitations can be generated and subsequently converted into light in an ultra-cold atomic gas, with no more than a single excitation retrieved from the entire mesoscopic ensemble of atoms in the limit of strong interactions. This system will be relevant for studies of dynamics and disorder in many-body systems with tunable interactions, and for realization of scalable quantum information networks.